EVIDENCE FOR THE HYPERSENSITIVITY OF LUMBAR SPLANCHNIC AFFERENTS IN IRRITABLE-BOWEL-SYNDROME

Background/Aims: The pathways underlying rectal hypersensitivity to ba lloon distention in patients with irritable bowel syndrome (IBS) are n ot known. The aim of this study was to characterize the involvement of sacral and thoracolumbar afferents in the perception of rectal disten tion. Methods: Rectal balloon distention was performed in 15 normal co ntrol subjects, 6 patients with spinal cord injury, and 50 patients wi th IBS using a slow-volume ramp (40 mL/min) or rapid phasic step diste ntion. Additional studies were performed in the presence of 2% intrare ctal lidocaine. Results: Patients with spinal cord injury with lesions below T7 reported sensations only during phasic distention. Sixty per cent of patients with IBS (n = 50) were hypersensitive for discomfort during phasic distention, whereas only 4% were hypersensitive during r amp distention. Less than 15% of patients were hypersensitive for the sensation of stool. In normal patients, lidocaine increased thresholds in response to slow ramp distention by 40%-70% but had no effect on p erception in response to other types of distention. Lidocaine had no e ffect on (1) thresholds in response to either ramp or phasic distentio n in normosensitive or hypersensitive patients with IBS or (2) the rat e of receptive relaxation or rectal compliance in any group. Conclusio ns: Rapid phasic distention preferentially stimulates splanchnic affer ents. Hypersensitivity of these afferents in patients with IBS is unaf fected by mucosally applied lidocaine.